1. Field of the Invention
The present invention relates to a hybrid vehicle equipped with a plurality of prime movers for running the vehicle.
2. Related Art
In the prior art, there have been developed a hybrid vehicle which is intended to improve an overall efficiency by combining a plurality of prime movers while exploiting the merits and compensating the demerits of the individual prime movers. One example of this hybrid vehicle is disclosed in JPA-7-186748.
The hybrid vehicle, as disclosed, is equipped with an engine and a motor-generator as the prime movers. The motor-generator is given a power running function to convert an electric energy into a kinetic energy, and a regenerative function to establish a regenerative braking force by converting a kinetic energy into an electric energy.
Moreover, the hybrid vehicle is constructed such that the drive force of the engine is transmitted either the front wheels or the rear wheels whereas the drive force of the motor-generator is transmitted to the wheels to which is not transmitted the drive force of the engine.
On the other hand, this hybrid vehicle is equipped with a controller for controlling its running state. To this controller, there are inputted a variety of signals for indexing the running state, such as the RPM of the engine, the throttle opening, the steering angle, the stroke of depression of the brake, the stroke of depression of the accelerator pedal or the gear position. The motor-generator is controlled by this controller on the basis of those signals.
In a straight running state or a running state at a small steering angle of the hybrid vehicle, for example, the drive force at an acceleration or the braking force at a deceleration is detected. Moreover, a shortage of the drive force, if detected, is assisted with the drive force of the motor-generator. On the other hand, a shortage of the braking force, if detected, is assisted with the regenerative braking force of the motor-generator.
However, what is done by the hybrid vehicle disclosed in the aforementioned Laid-Open is only to assist the shortage of the drive force of the engine or the braking force of the vehicle by the motor-generator. In short, no consideration is taken into the transient situation which accompanies the changes in the acting states of the engine and the transmission connected to the engine. Therefore, it cannot be said that the output of the motor-generator, as used in parallel with the engine, functions sufficiently for all the various situations that will occur from the start to the end of the run of the vehicle. This exerts a restriction upon the improvements in the running performance, the drivability or the riding comfort.